"I wouldn't be here without such generosity," Jobs said.
During the early moments of the event, the CEO outlined an update to Apple's iTunes software. Apple also issued a minor update to the iPhone software.
Jobs had not appeared at such an event since last October. He bowed out of his usual keynote at the year's largest Mac trade show in January and went on leave shortly thereafter.
Jobs disclosed in August 2004 that he had been diagnosed with - and cured of - a rare form of pancreatic cancer called an islet cell neuroendocrine tumor. Last year, he appeared increasingly thin, sparking speculation that his cancer had returned, though Apple attributed his weight loss then to a common bug.
On Jan. 5, 2009, Jobs said he had a treatable hormone imbalance and that he would continue to run the company. He went on leave the following week, saying his medical problems were "more complex" than he had thought. Apple's chief operating officer, Tim Cook, took over daily duties. Jobs returned to work this summer.